1. Field of the Invention
The present invention relates generally to an automotive shock absorber strut assembly for use in an automotive suspension. More particularly, the present invention relates to a shock absorber strut assembly which utilizes the unsprung vehicle mass to overcome breakaway friction in the strut.
2. Disclosure Information
Automotive suspension struts have two primary functions: to provide structural support and to permit hydraulically damped suspension motion. Typically, the strut is rigidly mounted to a wheel carrier at one end and pivotally mounted to the vehicle chassis at its other end. As used herein, the term "chassis" refers to either a conventional vehicle chassis or to a conventional unitary chassis and body construction and is intended to include vehicle structure and components connected to or supported upon the chassis structure and forming part of the sprung mass of the vehicle Also, the term, "sprung mass" refers to the body or chassis of the vehicle while "unsprung mass" refers to the roadwheel assembly, its associated rotating members as well as locating members such as suspension arms, etc. The mounting geometry of the strut relative to the wheel carrier causes radially directed sideloading of strut piston and rod bearing. This sideloading is undesirable inasmuch as the static friction resulting therefrom increases the force necessary to initiate sliding of the piston within the strut and, therefore, correspondingly increases the transmissibility of road-induced vibration from the wheel to the chassis of the vehicle when an obstruction is encountered on the roadway surface. During this strut binding, the desired damping action of the suspension does not occur. The force necessary to initiate sliding of the piston within the strut is also known as a breakaway force.
Attempts to minimize this undesirable static friction have resulted in various strut configurations. For example, U.S. Pat. No. 3,573,880 discloses a strut wherein the spring is eccentrically mounted about the strut. U.S. Pat. No. 4,615,537, assigned to the assignee of the present invention, discloses another design for reducing the static friction in a strut. The '537 patent discloses a telescoping strut including means for reducing static friction within the strut by causing either the upper end, the lower end or both ends of the strut to be rotated outboard with respect to the axis of the strut. Although these solutions can result in reduction of the strut friction, neither of these designs utilize the unsprung vehicle mass to overcome the friction forces in the strut.
It is an advantage of the present invention to provide a suspension strut assembly which provides superior ride characteristics by allowing strut motion and energy storing spring deflection at a lower road force input than by conventional struts. Energy stored in the spring is not transmitted to the vehicle structure but is hydraulically damped by the strut.
These and other objects, features and advantages of the present invention will be apparent from the summary, drawings, detailed description and claims which follow.